Choosy supports the file if you drag the .url to the Choosy.app (which exists in ~/Library/PreferencePanes/Choosy 1.0.1.prefPane/Contents/Resources/Choosy.app)
Unfortunately it's not possible to open the file via "Get Info » Open With" as it is grayed out.
I guess it's just a matter of a few changes in Info.plist but I can't seem to get it to work.

It would be highly appreciated if we could get this to work with Choosy. :)

While the .URL format originated from Internet Explorer, it appears to be recognized by pretty much every browser I've ever used on both Mac and Windows. It is because of this cross platform compatibility that I tend to use it in many situations.

The syntax is quite simple and is explained in this entry on MacOS X Hints: http://www.macosxhints.com/article.php?story=20040111200114634

One of the commenters there also posted a simple AppleScript for creating .URL files. This can be easily integrated as a service for Safari under Mac OS X 10.6 using Automator.

I'd also love to see support for this format implemented in a future version of Choosy.

I believe .url files are proprietary Windows Internet shortcuts. mainly because the moment I installed a demo version of crossover it wanted to open all .url files. It would probably require a completely different program. The mac version of .url files are .webloc (or something like that) files.